To assure high quality solder joints and avoid damage to sensitive electronic components during production procedures, it is important that various soldering iron operating parameters be maintained within acceptable limits. This fact has been widely recognized and has motivated the adoption of several standards and specifications:
DOD-STD-2000-1B PA1 DOD-HDBK-263 PA1 WS 6536E-2 PA1 MIL-S-45743E PA1 MIL-STD-2000 1989.
The standards and specifications require measurement of soldering iron tip temperature, tip voltage to ground and tip resistance to ground.
One prior art device, Wahl, U.S. Pat. No. 4,878,016, discloses an apparatus for measuring all three parameters. Wahl uses a single sensor, a thermocouple, for making all three measurements. Because the sensor is a thermocouple, the temperature of the soldering iron tip causes a temperature induced voltage when measuring tip voltage to ground and tip resistance to ground. This temperature induced voltage is typically 20 mV to 50 mV depending on the thermocouple type. The tip voltage to ground limit in several of the standard is 2 mV. It is not possible to measure tip voltage and ground without compensating for temperature induced voltage. The temperature induced voltage introduces errors of 10% or more when measuring tip resistance to ground. The Wahl apparatus shorts the thermocouple wire ends to eliminate the effect of the temperature induced voltage.